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Salinization is considered a significant threat to soil ecosystem and plant growth in arid and semiarid regions. Soil microorganisms are supposed to be essential in relieving soil salinization and enhancing plant salt tolerance. However, although the responses of soil fungal diversity and community structure to salt stress have been investigated, major knowledge gaps remain in the interactions and community assembly of abundant and rare fungal taxa, and fungal functional characteristics under different salt intensities. Here, next-generation sequencing technology were used to investigate the response of all, abundant and rare fungal taxa to salt stress in arid and semiarid regions. The results demonstrated that high salt stress reduced the complexity and stability of fungal networks and increased fungal collaborations. Rare taxa held a key position in the co-occurrence network and exhibited greater proficiency in collaborating with intermediate and rare taxa, thereby augmenting the resistance of the community and maintaining its stability. Notably, with increasing salt stress, the importance of rare taxa gradually enhanced, while the importance of abundant taxa decreased. Moreover, fungal communities were manipulated by stochastic processes under salt stress, while were also influenced by deterministic processes (heterogeneous selection), especially for rare taxa. Furthermore, low salinity conditions promoted the colonization of saprophytic and symbiotic fungi and inhibited the growth of pathogenic fungi. Functional groups associated with fungal parasite-soil saprotroph-undefined saprotroph function were extremely sensitive to soil salinity and exerted a pivotal influence in sustaining community stability. Our findings may broaden our understanding of how abundant and rare fungi react to salt stress, making it easier to forecast the possible loss of biodiversity due to soil salinization, and offering microbial references for the development of saline-alkaline soil. [Display omitted] • Fungal networks were less stable but more collaborative under salt stress. • Rare taxa were more robust in sustaining community stability than abundant taxa. • Rich and rare taxa's importance gap in sustaining network increased as salinity rose. • Stochastic processes gradually dominated community assembly as salinity increased. • Heterogeneous selection contributed more to rare taxa assembly than to abundant taxa. [ABSTRACT FROM AUTHOR]

• Soil salinity negatively affected soil bacterial diversity. • The community structure in solonchak was simpler and more prone to damage. • Rare taxa were as important as abundant taxa for co-occurrence network stability. • Community assembly was gradually dominated by stochasticity as salinity increased. Soil salinization has become the most expansive form of soil degradation in arid and semiarid regions, and the management of soil salinization is imperative for achieving sustainable development. Soil microorganisms are supposed to play an integral role in controlling soil salinization, and the effects of high-salt environments on microbial community have been widely investigated, but there is currently limited comprehensive study on taxon co-occurrence patterns and assembly processes under different salt intensities. Here, based on high-throughput sequencing technologies, we analysed bacterial community structure and assembly mechanism under salt intensity in arid and semiarid regions. The results demonstrated that bacterial diversity was negatively correlated with soil salinity, and community structure also varied with changes in salt intensity. Solonchaks (soils with high soluble salt accumulation) had the lowest average degree of bacterial co-occurrence network, and there was a lower level of connectivity and correlation among bacteria in solonchaks compared to other salt-affected soils. The highest competitive connections among soil bacteria were detected in light-intensity saline soils, whereas overall collaborative connections increased with soil salinity. For co-occurrence network stability, the rare taxa (with each taxon's relative abundance < 0.1%) were more essential than the abundant taxa (> 1%). As soil salinity increased, stochastic processes gradually dominated the community assembly, and the dispersal limitation contributed from 45.18% to 58.73%. These findings offered valuable information about how soil salt intensity affected soil bacterial community and would be useful in controlling soil salinization. [ABSTRACT FROM AUTHOR]